Porcelain bonding dental gold alloy

ABSTRACT

A DENTAL GOLD ALLOY USED FOR BONDING TO DENTAL PORCELAINS FOR CAPPING TEETH AND SIMILAR PURPOSES CONSISTING ESSENTIALLY OF APPROXIMATELY BY WEIGHT OF 67.7% GOLD, 11.6% PLATINUM, 16.7% PALLADIUM, 1.3% RUTHENIUM, 2% SILVER, 96% TIN AND .1% COPPER. THE ALLOY IS CHARACTERIZED IN HAVING A MELTING POINT OF APPROXIMATELY 2400 DEGREES F. AND HAVING A COEFFICIENT OF EXPANSION CLOSELY APPROXIMATING MOST COMMERCIALLY AVAILABLE DENTAL PORCELAINS, WHICH MAY BE ADJUSTED FOR PERFECT COMPATIBILITY. IN ADDITION, THE ALLOY IS RELATIVELY FREE OF ANY TENDENCY TO GAS, OXIDIZE OR DISCOLOR DURING BAKING, AND IS CAPABLE OF GREATER ELONGATION THAN PRIOR ART ALLOYS.

United States Patent Int. Cl. C22c 5/00 US. Cl. 75-165 1 Claim ABSTRACTOF THE DISCLOSURE A dental gold alloy used for bonding to dentalporcelains for capping teeth and similar purposes consisting essentiallyof approximately by weight of 67.7% gold, 11.6% platinum, 16.7%palladium, 1.3% ruthenium, 2% silver, .6% tin and .1% copper. The alloyis characterized in having a melting point of approximately 2400 degreesF. and having a coefiicient of expansion closely approximating mostcommercially available dental porcelains, which may be adjusted forperfect compatibility. In addition, the alloy is relatively free of anytendency to gas, oxidize or discolor during baking, and is capable ofgreater elongation than prior art alloys.

This invention relates generally to the field of metallic alloys, andmore particularly to a gold based dental alloy of a type used inconjunction with dental restorations.

In order to obtain a proper cosmetic appearance, it is common practiceto cap natural teeth by cementing or bonding a gold tooth to a preparedstump of the natural tooth lying therebeneath. To give the cap a naturalappearance, a porcelain jacket is bonded to the cap, the porcelain beingcapable of color tinting prior to baking to duplicate the color of thenatural teeth of the user. During fabrication, the metallic part of thecap is cast in an investment by the so-called lost wax process, andafter casting the outer surfaces of the cap are coated with ceramicfrits which are subsequently baked upon the cap. The usual practice isto apply a first coat to obtain completely opacity which is baked at atemperature below glazing temperature, and one or more subsequent coatsare applied to obtain the desired tint and contour.

Many problems have accompanied the practice of the above technique. Mostalloys in present use are either platinum based or gold based, and owingto different coefficients of expansion, it has been a common practicefor manufacturers to supply porcelains which are specially prepared tohave a mating coefficient of expansion, so that with baking, no crackingin the porcelain occurs, and a uniform bond with the metal is obtainedover the entire mating area.

The platinum based alloys melt at approximately 2800 degrees F. orhigher. These alloys normally contain large amounts of palladium whichis the cheapest of the noble metals. Unfortunately, it is also a veryunstable metal when porcelain is baked thereupon. It tends to gas underthe porcelain, causing poor bonding. Because of the presence of ferricmetal hardeners, the alloy also oxidizes, causing not only defectivebonding, but discoloration of the porcelain.

Gold based alloys are somewhat superior in this respect, but, again,owing to the presence of ferric hardeners oxidation and accompanyingdiscoloration still occur. In an attempt to overcome these difiiculties,some manufacturers recommend the use of a metallic bonding agent to beapplied to the casting before application of the porcelain. Thisprocedure adds to the cost of manufacture, and is not always successful.Another procedure widely followed is a so-called de-gassing bakingbefore the application of the porcelain, in which the casting is heatedin the absence of the porcelain to avoid checking or cracking of theporcelain when it is subsequently baked to its maturity.

The problems are complicated by other factors, most of which aretraceable to the fact that the metal must be reheated after initialcasting. The firings of successive coats of porcelain tends to causedistortion in the casting therebeneath, so that the caps no longerconform to the original invested wax pattern from the standpoint of fitwhen they are installed in the mouth of the user. This is particularlytrue in those alloys where the amount of base metal additions has beenreduced in order to avoid oxidation and discoloration. The softening ofthe metal has a deleterious effect on the strength of the alloy. Currentgold based alloys lack the ductility (due to lack of suitable hardeningagents) to permit the fine marginal seals required without chipping orflaking.

It is therefore among the principal objects of the present invention toprovide an improved gold based dental alloy in which the above mentioneddisadvantages have been substantially eliminated.

Another object of the invention lies in the provision of an improvedgold based dental alloy which offers a coefiicient of expansion withheat compatible to that of a large number of commercially availabledental porcelains.

Yet another object of the invention lies in the provision of an improveddental alloy of the class described which may be relatively free of anytendency to gas, oxidize or discolor with baking.

A further object of the invention lies in the provision of an improvedgold based dental alloy, in which the hardening constituents are of anon-ferrous type, thereby eliminating the deleterious effect of ferroushardeners.

These objects, as well as other incidental ends and advantages, willmore fully appear in the progress of the following disclosure, and bepointed out in the appended claim.

In accordance with the invention, a dental alloy is prepared inaccordance with the following formulation, the percentages ofingredients being by weight, and are approximate.

EXAMPLE 1 Percent Gold 67.7 Platinum 11.6 Palladium 16.7 Ruthenium 1.3

Silver 2.0

Tin p 0.6 Copper 0.1

As will be readily observed, gold comprises the major constituent in thealloy, with platinum present in a proportion of slightly less than 1 to7. This will result in a melting temperature of the alloy ofapproximately 2400 degrees F. It can be adjusted upwardly by slightlyincreasing the percentage of platinum as compared to gold, andcorrespondingly can be lowered by decreasing the amount of platinum inrelation to gold. Palladium comprises slightly under 17%, and isemployed principally as a filler, to slightly decrease the total cost ofthe alloy. Palladium also aids in hardening the gold (due to solidsolution hardening) and provides together with the platinum a medium forthe ruthenium to aid in hardening. This element does not cause oxidationin the alloy during casting, or subsequent baking, and thus, gassing,oxidation and discoloration are avoided. The relative trace amounts ofcopper and tin enhance the toughness of the alloy, permitting it to bethinned out to a greater degree before porcelain is baked on thecasting. This allows for more room for the porcelain, without weakeningthe metal framework.

Since the alloy is essentially a gold type, it may be cast usinginvestments normally used for casting that metal, thus the expansion ofthe metal and the investment being much more closely matched, theresultant fit of the cast part is more accurate than that normally foundwhen using platinum type castings.

As has been mentioned, it is possible to modify existing commercialporcelains so that the same will have substantially the same coetfecientof expansion with heating as the alloy. This is accomplished by mixingsmall portions of the patching type glaze supplied with the regularporcelain in varying amounts, the precise amounts dependent upon theparticular porcelain being used. Most commercial porcelains mature attemperatures ranging from 1750 degrees F. to 2000 degrees 'F., thehighest maturity value being 400 degrees below that of the melting pointof the alloy.

Because the alloy is essentially gold, soldering of joints is made withgold without difliculty, or gold alloys.

I wish it to be understood that I do not consider the 16.7% palladium,1.3% ruthenium, 2% silver, 0.6% tin and 0.1% copper.

References Cited UNITED STATES PATENTS 1,449,154 3/1923 Vidcon 75--165 X2.050,040 8/1936 Coleman et a1. 75l65 2,980,998 4/196'1 Coleman 'et al.75165 X L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, AssistantExaminer US. Cl. X.R. 75-172

